Spark-plug



F. M. FU'RBER'.

SPARK PLUG.

APPLICATION FILED JAN. 2|. I918.

1,323,36Q I IIQIIIQII Dec. 2,1919.

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FREDERICK M. FURBER, OF REVERE, MASSACHUSETTS.

SPARK-PLUG.

Specification of Letters Patent.

Patented bee. 2,1919.

Application fileii January 21, 1918. Serial No. 213,021.

1 0 all whom it may concern:

Be it known that I, FREDERICK M. FUR- nnn, a citizen of the United States, residing at Revere, in the county of Suffolk and-State of Massachusettes, have invented certain im- -provements in Spark-Plugs, of which'the following description, in connection with the accompanying drawings, is a specification, like reference characters on the drawings indicatino like parts in the several figures.

Spark in internal combustion engines comprise a metallic shell constructed to be threaded into an aperture in the engine cylinder, an insulator mounted in said shell and a pair of electrodes electrically separated by the insulator. The most serious problem in the manufacture of devices of thiskind concerns the mounting of the insulator in the shell. These insulators usually are made of porcelain so that they are relatively fragile and the usual commercial constructions and methods of manufacture are open to the objection that they break a substantial percentage of the insulators during the process of manufacture and that they frequently result in mounting the insulator in such a manner that it is under internal strains that cause it to break very easily while in use, either due to a relatively light blow which it should be able to successfully withstand, or due to strains set up by changes in temperatures to which it is subjected while in use.

A further problem involving the mounting of the insulator in the shell to which at tention has been especially directed by the trade in recent times is that of making the plug as tight. Insulators whether made of porcelain or other materials are notabsolutely uniform in shape and dimensions, and this is particularly true of porcelain insulators because they tend to warp in the baking operations. Consequently, it is difficult to mount these insulators in their shells by any methods capable of adoption in commercial manufacture so that they will-be absolutely gas tight when subjected to the high'pressure conditions and the wide range pf temperatures which they have .to withstand in actual use.

The present invention is concerned par- I tic'ularly with the'probl'ems just described and it aims to devise a spark plug construction that will solve these difiiculties.

The invention will be readily understood from the following descr ption, when read plugs of the type commonly used in connection with the accompanying drawmgs, and the novel features will be particularly pointed out in the appended claims.

Referring now to the accompanying draw.- irlgs7 Figure 1 is a view in side elevation of a spark plug embodying this invention;

Fig. 2 is a central, vertical, cross sectional view showing the spark lug of Fig. 1 mounted in an engine cylin er; F 1g. 3 1s a vertical, cross sectional view of part of the spark plug showing one step in its'process of manufacture; and

Figs. 4, 5 and 6 are side views of different constructions of shell parts used with a given body to make different sizes of spark plugs.

The construction shown comprises a shell consisting of a body 2 and a sleeve 4. The body may be made out of hexagonal bar stock by turning'ofl' a part of thev material from a piece of the required length to fornr a cylindrical skirt 6, leaving the upper part .inits original hexagonal form so that a wrench may be conveniently applied thereto to screw the plug into or out of an engine cylinder. The piece of stock is then bored, provided solid stock is used, and is counterbored for a distance from its lower or inner tively, are formed at the upper and lower ends, respectively, of the body. 10.

The insulator is clamped in the shell by parts that'engage the shoulders-=16 and 18. The flange 8 forms a seat for-the upper shoulders 16 and the u per endof the sleeve 4 is shaped to engage t e lowei shoulders 18. Instead of having these 1 partsengage directly the shoulders ofthe insulatorit-is preferable to inter-pose" gaskets flt) and 252 between the upper and lower shoulders and, the parts that exert clamping pressure on them. I prefer to use a solid metal washer at 20 made, for instance, out of copper or a suitable composition, and ,a gasket of the copper asbestos. type, very commonlywused is threaded into the cap 24. of the engine cylinder 26i A relatively fine thread, preferably of the buttress type, is used, as shown in the drawings, and is cut left handed.

In assembling the plug, the body 2 may be placed in its inverted position in a fixture 28 having a hexagonal socket to fit the outer surface of the body 2. The gasket 20 may then be dropped into the body. The insulator next is set into the body and a gasket 22 is placed on the lower shoulder of the insulator. While the parts are in this position the sleeve 4 is threaded into the lower end of the body, a suitable wrench shaped to fit the threaded shank b of the sleeve and constructed to clamp this shank being used for this purpose, The wrench shown comprises an internally threaded collar 30 adapted to be threaded on to the shank b of the sleeve, this threaded portion being split longitudinall and tapered externally to fit an intcrna ly taperedportion of'the body 32 of the wrench. The parts 30 and 32 are threaded together so that as the wrench is turned to thread the sleeve into the body 2, the bushing 30 will be caused to grip the shank 6 very securely but will not injure the threads. A very long handle may be used on the wrench, or the sleeve may be threaded in by power mechanism, but sufficient force should be applied to the sleeve to cause it to. exert a very heavy pressure, say 4,000 or 5,000 pounds on the lower shoulder of the insulator. This pressure distorts the gaskets 20'and 22 until they accurately fit the space between the insulator shoulders and the members that bear against them. The gasket 22 becomes seated on the lower shoulder 18 long before-the pressure of the sleeve reaches its maximum and thereafter the sleeue slides on the gasket but the asket does not move with reference to the lnsulator. I find that this method of assembling produces an exceedingly tight joint at both shoulders of the insulator, the oint at the lower shoulder being exceptionally good. By using a buttress thread, as shownin the c rawings, any danger of splitting the lower end of the shell, which might be produced if a V-shaped thread were used, is avoided.

The construction of sleeve shown provides a shoulder 34 between the shank b and the head a... It is desirable to have this shoulder substantially flush with the lower end of the body 2 so that when the plug is in its normal position in the engine, as shown in Fig. 2, any leakage of the gas along the thread of the portion 6 may be prevented by placing skilled labor.

substantially overcomes the objections hereinbeforc described. The shell parts 2 and 4 may be made automatically in screw ma chines or turret lathes and may be assembled very easily and without the use of The percentage of leaky plugs is exceedingly small since there is practically always a gas tight joint, atthe bottom shoulder of the insulator and in a very high percentage of the plugs the joint at the upper shoulder also is'gas tight. By making the shoulder 30 flush with the lower end of the body 2, and using a gasket 30 underneath these shoulders as shown in Fig. 2, any attempt 'of the gas to creep along the thread on the shank of the plug is avoided. The pressure of the shoulder 30 on the gasket 36 also prevents gas that works along the thread of the shank b from continuing its travel along the thread betweenthe head of the sleeve 4 and the body 2 where it would find access to the space above the gasket 22 and would escape at the upper end of the plug if the joint between the shoulder 16 and the flange 8 happened to be leaky. This construction also prevents gas that might find its way past the gasket 22, in the same event of a leak at this joint, from traveling along the thread between the parts a,

I and'2 and escaping at the shoulder 34.

The use of a left hand thread between the head of the sleeve 4 and the bottom of the body 2 is an important feature. The plug usually is'turned into an engine cylinder by meansof an ordinary wrench. While the force exerted on the body 2 would tend to unscrew it from the sleeve, this force would be much too small to produce the slightest danger of starting the thread and thus relieving the pressure that clamps the insulator in its normal position. These plugs frequently freeze in a cylinder and in at- -tempting to getthem out the workman may have to use a heavy hammer on the wrench that he applies to the body 2, and if the body and sleeve were united by a right hand thread there would be considerable danger of starting this thread in attempting to remove the spark plug in this manner. It will be seen, however, that by using a left hand thread between the parts 2 and 4 the force exerted in unscrewing the plug from the cylinder, will tend toturn the sleeve 4 all the tighter into the body 2 and thus tend to increase the pressure exerted by these parts on the insulator.

inch pipe idiread.

neessso navli bandied wrench is ve into the body elir- .iding the plug into an e .ne oyiinde and since the thread between the bead of the sleeve and the body is much liner the i she isnread on the shank of the sleeve, iliere is nos the slightest denof sterbing the thread between the sleeve and she body While the plug is in use. in these are secured together so ti. iv be separated even be effort is made is do so special tools.

*iis eonsi tion also is ver eonvenient Irons. sobering stanopolns since :1- sbenflerd boo nd may be used .ie important commercial sings. it is merely necessary re and elisnge the 'shread on in order to adept the, plug to 1 may of sizes. Figs. 4, 5 and d1 lei sent siz /les of sleeve ivliioh in body 2 shown in Fig. s, one heads a of ell these sleeves are same diameters and have the same tlireac out on them. see shanks 5, however,

are ell. d fierenfc. in Fig. i, the shank is e seven-eigiiiis inch standard :Bhreed, in Fig.

5, e 111655116 thread, end inIFig, 6, a one-half These three are the most common co mercial sizes,

"While the best embodiment of the invention of am in pre eni; aware, it is obvious this embodiment may be modified in deeeils of sense-suction While still E ng size essential prinoipies and charof the in enbion. The invention fiere ore not ill Mel. to embodiment 1 reeise form shown,

eat 1 claim as new, is: 1. A snarl: plug GOlfzlPIlSlIlg a body eonssrneted to receive a Wrench, :1 sleeve having a left sand threaded part screwed into the lower end of said body and a right hand *1 e dimensions of the shank por- I nave lierein shown and described gagemeni Wish an engine cylinder, en insulator having upper and lower should s 6D clamped between said flange and up end of said sleeve, and gaskets interposed between said shoulders and the re t. paris in clamping engagement \vl 3. A spark plug, eon'iprising a be sleeve, said sleeve and body liavi'n hand threaded portions in engagement w th each other byrneans oi which they are se cured together, end an insulator secure said body by said sleeve, said sleeve he a right hand threaded portion pro' below said body and adapted to be ed into engine cylinder.

A spark plug comprising s body constructed to receive a Wrench whereby the plug may be screwed into or out of an en-' gins cylinder, a sleeve, said sleeve bed" he ing, cooperating left hand threaded tions in engagementvvibli each other by means of which they are secured to -"li and an insulator mounted in said bod; having an enlargement with and shoulders she opposibe ends of se' largemeni, said body and sleeve beii vided with parts constructed be en siioulders blieroby clams sei in its operative posi sion in s id bod" said sleeve having a shank 33o for engagement with an engine o yi L In testimony whereof have signed name to this specification 

